How Would We Defend Against a Killer Asteroid?

by David Klemke on August 31, 2011

Earth is constantly being bombarded with all sorts of things from space. The sun constantly smashes us with solar winds and radiation, asteroids are constantly making their fiery descents and every so often we’ll have one of our own bits of equipment come back down once its reached the end of its life (or sometimes, sooner). Thankfully our atmosphere does a pretty good job of breaking these things up before they reach the ground and most of the time debris from space lands in an unpopulated area, causing little to no harm. Still there’s evidence littering our planet that tells us that large objects from space make their way down to the surface, often with very deadly consequences.

Probably the most famous piece of evidence to support this, even though people don’t usually know it’s name, is the Chicxulub crater on the Yucatan peninsula. This is the crater that is currently believed to be responsible for the mass extinction event that happened approximately 65 million years ago, the one that wiped out the dinosaurs. The impactor, a fancy name for the asteroid that made that giant crater, was estimated to be about 10KM in diameter. The collision has been estimated to have a total energy output of something like 96 teratons of TNT, 2 million times more powerful that the largest nuclear weapon ever detonated. With that kind of power being unleashed it’s then very plausible that it was responsible for the extinction of many species.

The most recent example we have of something like this, although many orders of magnitude less severe, is the Tunguska event which happened in Russia back in 1908. Whilst not technically an impact from an asteroid (or comet, possibly), it is believed that the Tunguska asteroid exploded about 5~10KM above the surface, it still managed to level an area of over 2,000 square kilometres. That’s still powerful enough to take out a major metropolitan area however, so you’d hope that we’d have some strategies for dealing with potential events like this.

Turns out, we do.

Now many people would say “Why wouldn’t you just nuke the bastard” figuring that our most powerful weapon would be more than enough to vaporize a potential threat before it could materialize. The thing is though whilst nuclear weapons are immensely powerful they derive much of their power from the blast wave that they create upon detonation. In space however there’s nothing for them to create a blast wave with so much of the nuke’s devastating power is lost, leaving just the thermal radiation to do its work. Depending on the type of asteroid¹ it will either make the problem worse or simply do nothing at all.

The better option is something called a Gravity Tug, a specially designed spacecraft launched well in advance of the potential impact event to steer the asteroid off course. In essence they’re a simple idea the spacecraft simply approaches the asteroid and then stays next to it, using ion thrusters to keep a set distance between them. Whilst the gravitational effect of the spacecraft on the asteroid is minuscule over time it adds up to be enough to steer the asteroid away from its crash course with earth. Indeed this exact idea is being proposed to deflect the potential impactor Apophsis who’s got a small chance of hitting earth in 2036. Of course this only works for asteroids we know about but our tracking is good enough now that it’s quite hard for a potential disaster causing asteroid to slip through unnoticed.

When it comes down to it having an asteroid cause significant damage is a distinctly rare event with our first line of defence (our atmosphere) doing a pretty good job of breaking up would be impactors. Still it’s good to know that despite the vanishingly small possibility of such a thing happening we’re still prepared for it, even if it means having to launch something years in advance. Maybe we’ll eventually be able to modify that technology to be able to capture asteroids in our orbit so we could utilize them as bases for further operations in space. I’m not holding my breath for that though, but it’s a nice fantasy to have none the less.

¹There are 3 main types of asteroid. The first is basically solid rock compressed together, so the asteroid is one solid object. The second is a collection of rubble that’s held together by the tenuous gravity between all the small fragments. The last are iron asteroids which are solid lumps of metal, which are the really scary ones.